Starting yesterday, merchants have the option of passing the credit card fees they pay to people like Visa and Mastercharge, on to the customer except in the 10 states which prohibit the practice.
The fee ranges from 1.5% to 3% with the larger stores, like Wal-Mart, able to negotiate the lower fees while small merchants are usually stuck paying more.
Merchants don't have to add the charge. It's purely optional like some gas stations charging different prices for cash and credit.
The fact that a fee is going to be charged is supposed to be clearly posted near the checkout and also on the receipt. These fees do not apply to debit cards and obviously not to cash.
I use charge cards for convenience and to collect the cash back points. If stores start charging me extra, I'll simply stop using them. I'll also stop shopping where the charges are being assassed if I have an option. If I go to a gas station that charges different prices for cash and credit, I pay in cash. If I have to shop at a store that charges to use a charge card, I'll either use cash or my debit card.
Expect to see this being phased in gradually to let you get used to it. The bigger stores, that compete on price, will be the last to institute the charge but I'm betting within 10 years every store will be hitting you with the extra fee and most people will simply pay it.